The present invention relates generally to equipment for processing semiconductor wafers. More particularly, the present invention relates to an air platen used to support a linear belt during the chemical mechanical polishing of semiconductor wafers.
Chemical mechanical polishing (CMP) is used for planarizing semiconductor wafers during processing of the wafers. Because semiconductor circuits on wafers are commonly constructed in layers, where a portion of a circuit is created on a first layer and conductive vias connect it to a portion of the circuit on the next layer, each layer can add or create topography on the wafer that must be smoothed out before generating the next layer. In order to improve the manufacturability of the circuits on the wafer, many processing steps require planarizing the wafer surface. For example, to improve the uniformity of deposition of the conductive vias, the wafer is planarized prior to deposition to reduce the peaks and valleys on the surface over which the metal is deposited.
In conventional planarization technology, a rotating wafer carrier head brings the wafer into contact with a polishing pad rotating in the plane of the wafer surface to be planarized, and pressure is applied to a semiconductor wafer in order to support the wafer face down against a moving polishing pad. One type of polishing or planarizing apparatus is the linear polisher. In linear planarizing technology, an endless belt travels over two or more rollers. The wafer is placed against the moving polishing surface of the belt. An example of a linear polishing system is the Teres(trademark) CMP System manufactured by Lam Research Corporation, Fremont, Calif.
A key component of a linear CMP system is the air platen. The air platen provides a cushion of air via air channels to support the belt as pressure is applied to the wafer. However, existing air platen may not provide a cushion of air that takes into account variations in the wafer surface when it is placed against the belt surface, leading to a wafer that is not uniformly polished. If this occurs, there may be topography that is not removed from the wafer surface, or else the wafer surface may be planarized to the point where pitting will occur on the wafer surface.
Another problem that is associated with air platen is that the portions of the belt that support the edge of the wafer often themselves are not properly supported by the air platen. This may result in what is known as edge exclusion. Edge exclusion categorically is a portion of the wafer edge that does not receive the same degree of polishing action as the balance of the wafer. The result is a reduction of usable area for product production.
Accordingly, there is a need in the art for an improved air platen for CMP systems.
In order to address the need for improved planarization or polishing control by a wafer""s edge, a platen assembly for supporting a polishing member, such as a linear belt on a linear polishing apparatus, is described below. According to one aspect of the invention, an air platen assembly is disclosed that includes a platen having a plurality of concentric rings. Each ring has a plurality of openings in order to provide a cushion of air to a CMP belt, and at least one of the rings extends beyond an outer edge of a wafer to be planarized by the CMP belt. A support is attached with the platen, and has a plurality of air ports for pressurized air to pass to the rings of the platen. A gasket is positioned between the support and the platen, and has a plurality of cutouts that align with the openings and the air ports. Also included is a base that supports the support.
According to another aspect of the invention, an air platen is disclosed that includes a plurality of concentric rings. Each ring has a plurality of channels in order to provide a cushion of air to a CMP belt. Each ring, except for two inner-most rings, has a top quarter, a bottom quarter, a leading edge quarter, and a trailing edge quarter. Each of the quarters and the inner-most rings is an independent air passage for receiving a supply of pressurized air. At least one of the rings is oriented to extend beyond an outer edge of a wafer to be planarized by the CMP belt. One pressure regulator is connected with each of the inner-most rings, and three pressure regulators are connected with each of the remaining rings.
According to another aspect of the invention, the air platen includes eight concentric rings, with each ring having a plurality of channels in order to provide a cushion of air to a CMP belt. An outer six rings each has a top quarter, a bottom quarter, a leading edge quarter, and a trailing edge quarter. Each of the quarters and two inner-most rings are independent air passage for receiving a supply of pressurized air. There is one pressure regulator connected with each of the inner-most rings, and three pressure regulators connected with each of the six outer rings. One of the three regulators is connected with the top quarter and the bottom quarter, a second of the three regulators is connected with the leading edge quarter, and a third of the three regulators is connected with the trailing edge quarter of each of the remaining rings. In addition, there are two channels passing through the air platen, with each channel having a plurality of passages extending upwardly from the channel to a top surface of the air platen. At least one of the outer six rings extends beyond an outer edge of a wafer to be planarized by the CMP belt.